When external temperatures are low, a fuel cell system has a problem in that damage that may be possibly caused to pipes and valves when water generated inside the fuel cell system becomes frozen after the fuel cell system is stopped; another problem that also exists is the problem of insufficient progress of an electrochemical reaction due to obstruction of gas supply when activating a fuel cell the next time after frozen water has blocked a gas passage.
In light of the problems described above, processing for, making at least either one of anode gas (such as a fuel gas) and cathode gas (such as oxidant gas) supplied to the respective electrodes of a fuel cell enter a deficient state at the time of activation of the system, increasing overvoltage in part of the electrodes, and thereby increasing the temperature of the fuel cell (hereinafter referred to as “low-temperature countermeasure processing”) has been suggested (for example, see Patent Document 1).    [Patent Document 1] Japanese Patent Application Laid-Open (Kokai) Publication No. 2003-504807